Euphorbia capitellata |
Euphorbia melanadenia |
|
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capitate sandmat, head sandmat, head spurge |
red-gland spurge, squaw sandmat |
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Habit | Herbs, annual or perennial, with slender to thick and woody rootstock. | Herbs, perennial, with moderately to strongly thickened rootstock. |
Stems | usually ascending (but ranging from decumbent to erect), 15–50 cm, glabrous, strigillose, or pilose. |
ascending to erect, 5–20 cm, sericeous to appressed-villous. |
Leaves | opposite; stipules distinct, filiform or divided into 2–3 subulate-filiform segments, without dark, circular glands at base, 0.6–1.5 mm, pilose; petioles 0.6–1.3 mm, glabrous, pilose, or strigillose; blade ovate to narrowly ovate, 4–19 × 2–8 mm, base asymmetric, one side strongly cordate, other side rounded to slightly cordate, margins entire or serrulate (commonly nearly entire with few scattered teeth, often slightly thickened), apex acute, surfaces often with red spot in center, glabrous, pilose, or strigillose; weakly 3-veined from base, usually only midvein conspicuous. |
opposite; stipules distinct (lower side) and connate (upper side), linear, 0.5–1 mm, densely pilose; petiole 0.8–1.5 mm, tomentose; blade ovate, 1.2–5 × 0.8–2.9 mm, base asymmetric, hemicordate, margins entire, apex rounded to acute, surfaces tomentose; venation inconspicuous. |
Involucre | narrowly obconic to narrowly campanulate, 0.8–1.6 × 0.7–1.3 mm, glabrous or pilose; glands 4, yellow-green to pink or maroon, circular to oblong, 0.2–0.4 × 0.2–0.5 mm; appendages white to light pink, oblong to reniform or flabellate, 0.2–1.1 × 0.5–1.7 mm, surfaces glabrous, distal margin entire. |
campanulate, 0.6–1.1 × 0.7–1 mm, tomentose; glands 4, deep red to purple, elliptic, 0.3–0.4 × 0.4–0.7 mm; appendages white or becoming pink with age, oblong to flabellate, 0.4–0.7(–1) × 0.7–1.2 mm, distal margin entire or erose. |
Staminate flowers | 25–40. |
45–80. |
Pistillate flowers | ovary glabrous or pilose; styles 0.4–0.6 mm, 2-fid entire length. |
ovary tomentose, styles 0.5–0.8 mm, 2-fid nearly entire length. |
Capsules | ovoid to oblate, 1.3–1.9 × 1.4–2.1 mm, glabrous or pilose; columella 1.1–1.7 mm. |
ovoid, 1.4–1.8 × 1.4–1.7 mm, tomentose; columella 1.2–1.5 mm. |
Seeds | pink to pinkish gray, narrowly ovoid to narrowly ovoid-oblong, 4-angled or weakly 3-angled in cross section, 0.9–1.5 × 0.5–0.7 mm, irregularly dimpled, sometimes also with faint transverse ridges that do not pass through abaxial keel. |
gray to tan, oblong, 4-angled in cross section, 1–1.2 × 0.4–0.6 mm, smooth to wrinkled or alveolate. |
Cyathia | in dense, terminal capitate glomerules, with reduced, bractlike leaves subtending cyathia, at tips of main stems and short, leafy, axillary branches; peduncle 0.1–1.2 mm. |
solitary at distal nodes; peduncle (0.6–)1.4–1.9 mm. |
2n | = 14. |
|
Euphorbia capitellata |
Euphorbia melanadenia |
|
Phenology | Flowering and fruiting year-round in response to sufficient moisture. | Flowering and fruiting year-round. |
Habitat | Gravelly washes, rocky slopes, basaltic talus, disturbed roadsides, primarily desert scrub, desert grasslands, riparian forests, rarely oak-juniper woodlands. | Rocky slopes, river washes, dry to wet soils. |
Elevation | 600–1600 m. (2000–5200 ft.) | 400–1400 m. (1300–4600 ft.) |
Distribution |
AZ; NM; TX; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Sinaloa, Sonora)
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AZ; CA; Mexico (Baja California, Sonora)
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Discussion | Euphorbia capitellata is a characteristic herb in the Sonoran Desert of southern Arizona, ranging east to extreme southwestern Texas. During peak flowering, plants are attractive due to the dense clusters of cyathia with well-developed involucral gland appendages. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Euphorbia melanadenia is similar in appearance to E. cinerascens, but E. melanadenia has conspicuous involucral gland appendages whereas E. cinerascens has inconspicuous appendages or lacks them entirely. Euphorbia melanadenia occurs in Arizona and southern California, whereas E. cinerascens is found only in southern and western Texas. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 262. | FNA vol. 12, p. 276. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > sect. Anisophyllum |
Sibling taxa | ||
Synonyms | Chamaesyce capitellata, C. pycnanthema, E. pycnanthema | Chamaesyce melanadenia |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 188. (1859) | Torrey: in War Department [U.S.], Pacif. Railr. Rep. 4(5): 135. (1857) |
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